Botany; Geotropism; Plants -- Irritability and movements
The effect of cutting off with a razor a thin slice from one side of
the conical apex of 14 young and short radicles was next tried. Six of
them after being operated on were suspended in damp air; the tips of
the other eight, similarly suspended, were allowed to enter water at a
temperature of about 65° F. It was recorded in each case which side of
the apex had been sliced off, and when they were afterwards examined
the direction of the curvature was noted, before the record was
consulted. Of the six radicles in damp air, three had their tips curved
after an interval of 10 h. 15 m. directly away from the sliced surface,
whilst the other three were not affected and remained straight;
nevertheless, one of them after 13 additional hours became slightly
curved from the sliced surface. Of the eight radicles with their tips
immersed in water, seven were plainly curved away from the sliced
surfaces after 10 h. 15 m.; and with
respect to the eighth which remained quite straight, too thick a slice
had been accidentally removed, so that it hardly formed a real
exception to the general result. When the seven radicles were looked at
again, after an interval of 23 h. from the time of slicing, two had
become distorted; four were deflected at an angle of about 70° from the
perpendicular and from the cut surface; and one was deflected at nearly
90°, so that it projected almost horizontally, but with the extreme tip
now beginning to bend downwards through the action of geotropism. It is
therefore manifest that a thin slice cut off one side of the conical
apex, causes the upper growing part of the radicle of this Phaseolus to
bend, through the transmitted effects of the irritation, away from the
sliced surface.
Tropaeolum majus: Sensitiveness of the apex of the Radicle to
contact.—Little squares of card were attached with shellac to one side
of the tips of 19 radicles, some of which were subjected to 78° F., and
others to a much lower temperature. Only 3 became plainly curved from
the squares, 5 slightly, 4 doubtfully, and 7 not at all. These seeds
were, as we believed, old, so we procured a fresh lot, and now the
results were widely different. Twenty-three were tried in the same
manner; five of the squares produced no effect, but three of these
cases were no real exceptions, for in two of them the squares had
slipped and were parallel to the apex, and in the third the shellac was
in excess and had spread equally all round the apex. One radicle was
deflected only slightly from the perpendicular and from the card;
whilst seventeen were plainly deflected. The angles in several of these
latter cases varied between 40° and 65° from the perpendicular; and in
two of them it amounted after 15 h. or 16 h. to about 90°. In one
instance a loop
was nearly completed in 16 h. There can, therefore, be no doubt that
the apex is highly sensitive to slight contact, and that the upper part
of the radicle bends away from the touching object.
Public-domain text, read in full here on John Shaqi.
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